Size a hot rich oil flash drum: dimensions, flash gas, and retention time, per GPSA 16.
| Parameter | Typical Range |
|---|---|
| Flash Pressure | 50–200 psig |
| Flash Temperature | 100–200°F |
| Retention Time | 3–10 min |
| L/D Ratio | 2.5–4.0 |
| KSB (Flash Drum) | 0.10–0.20 |
| Vapor Fraction | 5–25% |
Equilibrium K-values:
Light ends (C₁/C₂/C₃) from the GPSA / DePriester chart (McWilliams 1973 fit); the C₁₀–C₁₄ absorption-oil pseudo-component from the Wilson vapor-pressure equation, giving K ≪ 1 so the oil stays in the liquid.
Rachford-Rice Flash Equation:
Solved by bisection for vapor fraction V over the oil-dominated feed (oil carrier + dissolved C₁/C₂/C₃). Methane and ethane preferentially flash; propane and heavier remain in the oil.
Function: This single-stage hot rich-oil flash tank liberates dissolved light gases (C₁/C₂) at reduced pressure before the oil enters the purification still. This reduces vapor loading on the still and recovers fuel gas. Multi-stage flash regeneration (250–400°F) is covered in the engineering guide but is out of scope for this single-stage sizing tool.
Understand hot oil flash systems, absorption oil regeneration, flash drum design, and flash gas recovery
A hot rich-oil flash tank is a vessel where heated rich oil from an absorber is flashed at reduced pressure to release dissolved light gases (C₁, C₂) before entering the oil purification still. It is sized per GPSA Ch. 16.
The calculator computes real equilibrium K-values as K = Psat(Tflash)/Pflash — light ends (C₁/C₂/C₃) from the GPSA / DePriester chart (McWilliams correlation) and the absorption-oil pseudo-component from the Wilson vapor-pressure equation — then solves the Rachford-Rice equation by bisection for the vapor/liquid split and composition at the specified flash temperature and pressure.
Retention time ensures adequate liquid-vapor separation and typically ranges from 3 to 10 minutes depending on oil viscosity and flash severity. The calculator uses retention time with liquid flow rate to size the vessel.
Flash tank vessels are designed per ASME Section VIII for pressure containment. The calculator determines vessel diameter, length, wall thickness, and estimated weight based on design pressure and the Rachford-Rice flash results.